Wednesday, January 22, 2014

Kriss Kross Site Scripting in Ability Mail Server - CVE-2013-6162

Cross Site Scripting

Cross Site Scripting (XSS) is a type of attack where an attacker can have a legitimate website or web application send a payload, usually JavaScript, to their user's browsers. The user's browser will then receive this payload and execute whatever it may be. Essentially, the attacker is taking advantage of the fact that the browser is going to trust that whatever the web application is sending is trustworthy and will execute it with no questions asked. Cross Site Request Forgery (CSRF) is the opposite of this where the web application will trust that whatever actions the user's web browser is requesting to perform are trustworthy and will execute them with no questions asked. We'll get to CSRF in a later post. You can read more about XSS and its various flavors here.

Anyways, XSS is often disregarded as low impact because the quintessential XSS proof of concept is usually throwing up an alert box. Big whoop. Well, not so fast...It is number three on OWASP's Top 10 (CSRF is number 8) so there's gotta be more to it. Let's dig in.

CVE-2013-6162

CVE-2013-6162 is a XSS vulnerability I discovered in Ability Mail Server 3.1.1. It's a fairly simple XSS vulnerability to demonstrate, but I think it serves as a good example of what kind of impact XSS can have. After installing Ability Mail Server (AMS) and installing the webmail component of AMS, we created a victim account to do our testing on.

First things first, we will fuzz the various fields of an email. This can range from injecting JavaScript in the From, To, Subject, Date, etc. fields and seeing if you can trigger an alert box. Eventually we try injecting into the body of the email

Once we run that script we log in with the victim account and view the email.

Success! We've been able to get the browser to execute JavaScript of our choosing.

Now, the normal XSS attack involves dumping the user's cookie and attempting to login as the user via a replay attack. Unfortunately, I didn't get a cookie when I attempted this. So, what else could we do? I never attempted using BeEF via XSS, only through the demo site so I decided to check it out. BeEF is a tool that you can use to execute commands against a victim's browser. The main stipulation is that the user must load the hook.js script which allows all of the magic. BeEF is a really great tool and you can read more about it here. I updated my proof of concept to load the hook.js script, fired up BeEF in Kali, and fired away.

Upon opening the email...

Sweet!

I have not had the opportunity to load BeEF via XSS before so this was a new wrinkle.

While this CVE deals with XSS and violating the trust that a browser has in a website, I was able to leverage this vulnerability into a CSRF attack. I'll detail that in another post.

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